1. Field of the Invention
The present invention relates to an exhaust system of an internal combustion engine.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 60-27710 discloses a valve timing control device for controlling the timing of an opening and a closing of an intake valve. In this device, when the opening timing of the intake valve is advanced, a valve overlapping period, during which both the intake valve and an exhaust valve are open, is prolonged, and thus a problem arises in that an amount of air fed into a cylinder during an intake stroke is reduced because burnt gas remaining in the cylinder flows backward toward the intake port.